Currently, the capability required for a computer system is being increased, and functions required for a computer system are being complicated, irrespective of a general-purpose computer system such as a PC or an embedded computer system such as a cellular phone or a car navigation system.
In order to meet high performance requirements, an increased number of systems have a direct memory access controller (hereinafter referred to as a DMAC) operable to perform a high-speed data transfer without use of a microprocessor, or have a plurality of microprocessors or accelerators (dedicated hardware for processing a specific function at a high speed) that are operated in parallel.
Furthermore, a system running a plurality of software processes (hereinafter simply referred to as processes) in parallel under the control of a multitask operating system has commonly been used in order to achieve a complicated function.
When a plurality of processes are running in parallel on a computer system for which a high reliability is required, such as a vehicle-installed device or a medical device, it is essential to install a mechanism (hereinafter simply referred to as a protection mechanism) for providing such a protection that unauthorized access (reading or writing) to an address space, which is caused by a malfunction resulting from a logic bug or noise that is inherent in software of a process, does not destroy states of other processes. The state of a process refers to the content of a memory used by the process or the state of peripheral devices (including internal states).
Patent literatures on the related arts of existing computer systems and existing protection mechanisms of a computer system include JP-A 06-236300 (Patent Literature 1), JP-A 10-240623 (Patent Literature 2), JP-A 01-265341 (Patent Literature 3), JP-A 63-029849 (Patent Literature 4), JP-A 2007-011580 (Patent Literature 5), JP-A 11-501141 (Patent Literature 6), and the like.
Furthermore, non-patent literatures on the related arts include Infineon, TC1767 User's Manual V1.1, the Internet    <http://www.infineon.com/dgdl/TC1767_UM_V1.0.pdf?folderld=db3a3043156fd5730 115b892639c0e97&fileld=db3a30431be39b97011bff530d517bcd> (Non-Patent Literature 1), Collections of Standard Technology on the Internet <URL:    http://www.jpo.go.jp/shiryou/s_sonota/hyoujun_gijutsu/handoutai_ip/1-3-9.htm>(Non-Patent Literature 2), the manual as in Non-Patent Literature 1, p. 11-73(Non-Patent Literature 3), and the like.